1. Field of the Invention
This invention relates to the separation of undesirable gaseous components from a waste gas. More particularly, this invention relates to apparatus and methods wherein granular adsorbent material, such as activated coke or activated charcoal, is caused to flow through a waste gas, in a direction transverse to the direction of gas flow, to adsorb the undesirable components of the gas. The invention has particular utility in separating out sulfur dioxide and nitric oxides from the waste gas from electric power stations.
2. Description of the Prior Art
Gas purification apparatus has been provided wherein granular adsorbent material is supported as a fluidized bed which flows downwardly through a horizontally-flowing stream of gas containing undesirable components to be removed from the gas. In such an installation, the adsorbent at the top is relatively fresh, while the adsorbent nearer the bottom is increasingly loaded with impurities. This has presented a problem, because the gas in the top portions of the horizontally moving gas stream is effectively purified, while the gas in the portions nearer the bottom of the stream may be insufficiently purified. One solution that has been proposed to this problem is to direct the lower portions of the gas exiting from the adsorber into a second adsorber. However, this solution is unsatisfactory because it increases both the construction costs and the quantity of adsorber required.
It also has been proposed to divide the flowing stream of gas unevenly in such a manner as to direct a proportionately greater quantity of the gas into the upper part of the downwardly-moving fluidized bed than into the lower part thereof. Such an arrangement however alters the rate of gas through-flow, resulting in pressure losses with adverse effects on the separation action. It also is known to increase the fluidizing speed at the gas entrance to the adsorber, such that the dust held at the entrance side by the adsorbent is more rapidly transported off so as to counter the effect of an increase in the pressure loss.